Published: 01 January 1979
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Cite this document
A foil test component (tapered box beam) consisting of hybrid graphite/epoxy skins and HY-130 steel spars was designed and fabricated. This design is representative of a hydrofoil strut/foil system having an approximate 25 percent weight savings compared to current metallic strut/foil systems fabricated entirely of steel with a yield strength of 900 MPa. Two identical box beams will be tested in the laboratory (one in air, the other in salt water) to assess the fatigue behavior of a typical graphite/epoxy structure under simulated sea loads and to compare its behavior with current metal designs.
The graphite/epoxy hybrid (T-300, GY-70 fibers) laminate selected for the skin material has been characterized; the elastic constants and ultimate strengths were in excellent agreement with the theoretical results predicted during the preliminary design phase. An in-depth joint evaluation was conducted as the next step of design verification. Each type of joint was modeled and tested statically and in fatigue. Although a maximum joint efficiency of 98 percent was developed in the I-beam tests, the scarf joint tests led to a 33 percent reduction in the design ultimate stress allowable for the composite material. One box beam has been successfully fabricated and assembled. A comprehensive nondestructive evaluation of the components and finished assembly reveal no detectable defects as a result of laminate fabrication or box beam assembly.
composite materials, fatigue tests, graphite composites, epoxy laminates, mechanical properties, nondestructive tests, joints, hybrid composites, ultimate strength, elastic properties, property prediction
Principal engineer/scientist, McDonnell Douglas Astronautics Company, Huntington Beach, Calif.
Structural engineer, David W. Taylor Naval Ship Research and Development Center, Bethesda, Md.